1. Field of the Invention
The present invention generally relates to a method of manufacturing a semiconductor device and, more particularly, to a method of manufacturing a semiconductor device having a post electrode as a mounting terminal.
Recently, as a semiconductor device has rapidly been miniaturized and given a higher density, mounting terminals thereof accordingly have been pitched narrowly. Especially for a CSP (Chip Size Package), the above-mentioned narrow pitch makes a serious problem when the CSP has mounting terminals provided on electrode pads formed on the periphery of a semiconductor element, because the semiconductor element has substantially the same size as the package itself.
In order to avoid the above-mentioned problem, mounting terminals and electrode pads are formed in an offset state so that the mounting terminals are formed in a matrix in a package. This structure requires wirings (hereinafter referred to as redistribution layers) to connect the mounting terminals and the electrode pads.
On the other hand, a semiconductor device is required to be manufactured at a low cost. Accordingly, in manufacturing a semiconductor device, the above-mentioned redistribution layers need to be formed at a low cost.
2. Description of the Related Art
Recently, wafer-level techniques have been applied in manufacturing a CSP-type semiconductor device, in which techniques redistribution layers (wirings) and a sealing resin are provided before dicing (separating into pieces) a wafer. Hereinbelow, a description will be given of a conventional method of forming a redistribution layer (a wiring) and providing a sealing resin at the wafer level.
FIG. 1 to FIG. 12 show a series of steps of manufacturing a conventional semiconductor device. As mentioned above, a wiring (a redistribution layer) 25 and a sealing resin 26 are provided before dicing (separating into pieces) a wafer 11. However, for convenience"" sake in showing and describing, FIG. 1 to FIG. 12 do not show the whole wafer 11, but magnify a part of the wafer 11 in the vicinity of an electrode pad 12.
An electronic circuit and an electrode pad 12 are formed beforehand on the upper surface of the wafer 11 (a surface on which the wiring 25 is to be formed). Also an insulating film 13 is formed so as to cover the upper surface of the wafer 11. The insulating film 13 has an opening formed at a position corresponding to the electrode pad 12 so that the electrode pad 12 is exposed from the insulating film 13.
In forming the wiring 25, firstly, an underlying metal film 14 is formed on the wafer 11 in the above-mentioned state, as shown in FIG. 1. The underlying metal film 14 is made of copper (Cu), and is formed by sputtering. The underlying metal film 14 is formed all over the wafer 11.
After the underlying metal film 14 is formed, a resist 15 made of an insulating material is provided on the underlying metal film 14, as shown in FIG. 2. The resist 15 has an opening 16 shaped according to the wiring 25 to be formed. Subsequently, a wiring film 17 is formed on the underlying metal film 14, as shown in FIG. 3, by electroplating using the underlying metal film 14 as an electrode and the resist 15 as a mask.
This wiring film 17 is made also of copper (Cu) as the underlying metal film 14. In the above-mentioned electroplating, the resist 15 is used as the mask so as to give the wiring film 17 a shape according to the wiring 25 to be formed.
After the wiring film 17 is formed, the resist 15 is removed, as shown in FIG. 4. Thereafter, a resist 18 is provided on the underlying metal film 14 and the wiring film 17, as shown in FIG. 5. The resist 18 has an opening 19 to form a post 20 therein.
Subsequently, the post 20 is formed in the opening 19, as shown in FIG. 6, by electroplating using the underlying metal film 14 as an electrode and the resist 18 as a mask. This post 20 is made also of copper (Cu) as the underlying metal film 14 and the wiring film 17. The post 20 is formed at a position corresponding to a position at which a solder bump 27 (a mounting terminal) is to be provided in a step described hereinafter.
After the post 20 is formed, an Ni film 21 is formed on the post 20, as shown in FIG. 7. Subsequently, an Au film 22 is formed on the Ni film 21, as shown in FIG. 8, so that the post 20, the Ni film 21 and the Au film 22 together form a post terminal 23.
After the post terminal 23 is formed, the resist 18 is removed, as shown in FIG. 9. Thereafter, a resist (not shown in the figures) is provided so as to cover the wiring film 17 (having the shape according to the wiring 25 to be formed) and the post terminal 23 for a patterning of the underlying metal film 14. Specifically, the underlying metal film 14 except a portion facing the wiring film 17 (having the shape according to the wiring 25 to be formed) is removed by etching, as shown in FIG. 10. This forms the wiring 25 on the wafer 11.
After the post terminal 23 and the wiring 25 are formed as above, the sealing resin 26 is formed over the wafer 11 by molding, as shown in FIG. 11. Then, the solder bump 27 as a mounting terminal is provided on the upper end of the post terminal 23 by, for example, a transferring process. Thereafter, the wafer 11 is diced into pieces so as to form a semiconductor device 10. FIG. 12 shows a part of the completed semiconductor device 10 in the vicinity of the electrode pad 12.
As described above, the wiring 25 and the post terminal 23 are formed by electroplating steps (see FIG. 3 and FIG. 6). However, using the electroplating steps to form the wiring 25 and the post terminal 23 necessitates an electric supply to be provided to a portion plated by a metal (copper in the above-mentioned steps) in electroplating.
The underlying metal film 14 shown in FIG. 1 is used to provide the above-mentioned electric supply in electroplating. Therefore, the underlying metal film 14 cannot be removed until all electroplating steps are finished. In other words, the underlying metal film 14 is removed after all the electroplating steps are finished. Specifically, in the above-described conventional method, the underlying metal film 14 is removed by etching shown in FIG. 10.
Therefore, until the underlying metal film 14 is removed, the sealing resin 26 cannot be provided. Accordingly, in forming metal members including the wiring film 17 and the post 20, a resist has to be provided and then removed each time. This complicates the manufacturing steps of a semiconductor device.
Specifically, in the conventional method shown in FIG. 1 to FIG. 12, the wiring 25 and the post terminal 23 need to be formed prior to the step of removing the underlying metal film 14 shown in FIG. 10. Accordingly, the resist 15 has to be provided in the step shown in FIG. 2 so as to form the wiring 25 (the wiring film 17), and then the resist 15 has to be removed in the step shown in FIG. 4. Also, the resist 18 has to be provided in the step shown in FIG. 5 so as to form the post terminal 23, and then the resist 18 has to be removed in the step shown in FIG. 9. Thus, the above-described conventional method requires two sets of steps of providing and removing a resist. This complicates the manufacturing steps of a semiconductor device.
Besides, using a copper (Cu) as a material forming the wiring 25 (the wiring film 17) entails a consideration for a migration. That is, although a copper (Cu) has a small electrical resistance, and thus has a good electric property as a wire, the copper (Cu) is prone to be affected by a migration so that arranging copper wires (the wiring 25) adjacent to each other causes a poor insulation. It is well known that coating the copper wire (the wiring 25) with another metal film such as a nickel (Ni) film effectively prevents this migration.
Considering when to perform such a coating step so as to coat the wiring 25 completely, forming the metal film before removing the underlying metal film 14 is too early, because the remaining portion of the underlying metal film 14 is exposed from the metal film when the underlying metal film 14 except the portion facing the wiring 25 (the wiring film 17) is removed. Therefore, the metal film needs to be formed to completely coat the wiring 25 after removing the underlying metal film 14. On the other hand, it is impossible to coat the wiring 25 with the metal film after the sealing resin 26 is provided. Consequently, in the above-described conventional method, the metal film for preventing a migration can only be formed in the step shown in FIG. 10.
However, if the metal film is formed in the step shown in FIG. 10, not only the wiring 25 but also the post terminal 23 are coated with the metal film. When the post terminal 23 is coated with the metal film such as a nickel (Ni) film, the solder bump 27 cannot surely be provided on the upper end of the post terminal 23 by a transferring process with a sufficient mounting intensity. This decreases the reliability of the semiconductor device 10. In short, the conventional manufacturing method does not provide an optimal opportunity to form the metal film for preventing a migration.
It is a general object of the present invention to provide an improved and useful method of manufacturing a semiconductor device having a post electrode as a mounting terminal in which method and device the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a method of manufacturing a semiconductor device having a post electrode as a mounting terminal which method can have simplified steps manufacturing the semiconductor device preventing a migration from occurring between wires thereof.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a method of manufacturing a semiconductor device, the method comprising the steps of:
forming a wiring electrically connected to an electrode pad formed on a substrate, the wiring extending on the substrate;
forming a post terminal by electroless plating so that the post terminal is electrically connected to the wiring; and
providing a sealing resin so as to cover the substrate except a position at which the post terminal is formed.
According to the present invention, since the post terminal is formed by electroless plating, an underlying metal film or an underlying wiring, which would be necessary in electroplating to provide an electric supply, does not have to be provided nor removed. This simplifies the steps of manufacturing a semiconductor device.
Additionally, in the semiconductor device manufacturing method according to the present invention, the step of providing the sealing resin may be performed before the step of forming the post terminal, and the step of providing the sealing resin may include forming an opening in the sealing resin so as to form the post terminal in the opening in the step of forming the post terminal.
According to the present invention, the post terminal can be formed by electroless plating using the sealing resin as a mask. Additionally, after the post terminal is formed by electroless plating, the sealing resin does not have to be removed to remove an underlying metal film or an underlying wiring that would be present under the sealing resin in electroplating to provide an electric supply. Therefore, the step of forming the post terminal does not need to include providing and removing a resist required in a conventional method. This simplifies the steps of manufacturing a semiconductor device.
Additionally, in the semiconductor device manufacturing method according to the present invention, the step of providing the sealing resin may include selecting an alkali-proof material to form the sealing resin.
According to the present invention, although an electroless plating solution used in electroless plating generally has a strong alkalinity, selecting an alkali-proof material to form the sealing resin prevents the sealing resin from deteriorating in electroless plating. Thus, the post terminal can surely be formed by electroless plating using the sealing resin as a mask.
Additionally, the semiconductor device manufacturing method according to the present invention may further comprise the step of forming a metal film on the wiring after the step of forming the wiring so that the wiring is coated with the metal film, wherein the step of forming the post terminal and the step of providing the sealing resin are performed after the step of forming the metal film.
According to the present invention, since the metal film is formed on the wiring after completion of the step of forming the wiring, the wiring is completely coated with the metal film without any portion of the wiring being exposed outwardly. Thereby, even though the wiring is made of a material disposed to a migration, the wiring is completely covered with the metal film so as to avoid a migration.
Additionally, in the semiconductor device manufacturing method according to the present invention, the wiring may be formed of copper (Cu).
According to the present invention, a copper (Cu), which has a small electrical resistance and thus has a good electric property as a wire, can improve the capability of the semiconductor device. It is noted that, even though the copper (Cu) itself is prone to cause a migration, the wiring formed of copper (Cu) is completely covered with the metal film so as to avoid a migration.
Additionally, the semiconductor device manufacturing method according to the present invention may further comprise the step of forming at least one metal film on the post terminal by electroless plating after the step of forming the post terminal.
According to the present invention, the metal film for the post terminal can be formed by electroless plating without using an underlying metal film or an underlying wiring to provide an electric supply, as in forming the post terminal. In addition, the metal film for the post terminal can be formed after the sealing resin is provided, because forming the metal film on the post terminal does not use the underlying metal film or the underlying wiring to provide an electric supply.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.